This invention is directed to an engine transient compensating circuit for sensing the start of a harmless overtemperature transient occurring in an engine, and for preventing the indication of an overtemperature condition when this overtemperature condition is harmless. The device has a temperature sensor, means for detecting the harmless overtemperature transient, and circuitry for generating a compensating signal which prevents an overtemperature indication when none is required.
Engines, particularly turbine engines, which are used in critical or industrial situations require the constant monitoring of operating temperature so that in the event the temperature exceeds safe limits, the engine may be shut down or the load decreased until engine temperature is reduced to a safe range. However, an engine may occasionally be required to operate for brief periods of time at loads or under other conditions which cause temperature to rise for a brief period of time, and then drop after the engine component expansion normalizes, or the increased load or other condition is removed. Such a brief temperature rise, so long as it is of relatively short duration and magnitude, is not harmful, is basically absorbed by the thermal mass of the engine, and may be ignored.
Presently available temperature monitoring systems are comprised of warning lights and/or gauges which signal an operator either by lights, sounds, needle movement or some other manner, that the engine temperature has reached a predetermined level considered high enough to merit such a warning. In the usual case, the operator then must make a quick decision whether to immediately reduce the operating stresses or power of the engine, shut the engine down completely, or to leave the conditions as they are to see if the temperature will drop as operating conditions change. This takes the attention of the operator and forces him to examine the various factors involved such as the magnitude of the temperature spike, the duration of the rise, and the time elasped since any prior overtemperature conditions. In a critical situation, this diversion of attention may cause the operator to lose track of other important matters which merit his consideration.
For example, a helicopter pilot may wish to gain altitude quickly under full load conditions, and in doing so, may subject the engine to a high load, causing the engine temperature to rise, but for only a relatively short period of time until the engine normalizes or the desired altitude is reached. The cockpit temperature monitoring devices presently available would register an overtemperature warning immediately requiring the pilot to reduce the power, when a predetermined high temperature is reached, without regard to the expected duration of the temperature spike or its relative magnitude. The helicopter pilot is then required to make a subjective decision whether to cease his climb immediately, or continue it for a time he feels is safe.
The circuitry of present invention is activated when a threshhold temperature is reached, and then monitors the magnitude of the temperature spike and its duration. Provided that the temperature does not exceed a predetermined maximum and does not last beyond a preset period of time, the engine transient compensating circuit generates a compensating signal which precludes the engine temperature indicators from displaying an over-temperature warning signal. The present invention also contains components which prevent it from operating more than once unless engine temperature first drops to a predetermined low safe value, thereby minimizing the possibility that a second or subsequent temperature rise would go undetected, causing a cumulative effect on the engine and possible damage.
Thus, the present invention prevents an overtemperature warning from being displayed unless it is actually necessary.